Unless the owner or the landlord permits it normally you can not make any permanent structural changes. A drop ceiling would be that. What is the issue with the current ceiling?

You can have bigger windows in your drawing room. The size can be 6'x6' on both the sides. The sill level can be at 2' if you like bay windows. Add one more window in your dining room. For the bedroom, you'll have to make the furniture plan first .For all the toilets, there must be ventilation at the height of 7' and the height of the ventilation can be 18". In the kitchen its the same as bedroom, you'll have to do the plan first. For more detail planning you can contact me at rupalgshah@hotmail.com.

Hello Rola, You can go for a slightly bigger one upto 21 inches. See if you likes sinks with drain board. Thanks, Amit Cornerstone Designs Bangalore

Kimberly, This seems to be appearing in Houzz India portal. Not sure if folks would have a complete view on the pricing at your geography. Thanks, Amit CORNERSTONE DESIGNS, Bangalore